This invention concerns a procedure for the co-ordination of at least two radar units in order thereby to achieve performance benefits. This invention also concerns a system comprising at least two radar units which are controlled in a co-ordinated way in order thereby to achieve performance benefits. This application is based on applications No. 9700111-9 and 9700112-7 filed on Jan. 17, 1997 in Sweden, the contents of which are incorporated hereinto by reference.
The performance of a radar unit and in particular of a reconnaissance radar is usually given in the form of its range. A suitable measurement of the range is the distance at which an approaching radar target is first detected by the radar unit with a particular probability.
An increase in the range can, for example, be achieved by means of an increase in the power output (average power) of the radar unit, by means of a larger antenna or by reducing the noise factor of the radar unit. An increase in a radar unit's power output usually leads to its output stage needing to be replaced by one or more larger output stages with higher output. This leads unavoidably to a larger cooling requirement for the output stage(s) and a higher power consumption which results in a need for a more powerful power supply. The costs and the space requirements increase rapidly. In certain applications, for example in an aircraft, there is only a predetermined limited space available for a radar unit. Radar applications where the radar unit must be located in a place with one or more physical restrictions, usually makes impossible any extensions of the radar unit in excess of the allocated space, the cooling capacity and/or the power supply.
It is already known that there is a co-ordination benefit if two or more radar transmitters co-operate by frequency division multiplexing with sufficiently separated frequencies. The radar receivers are designed so that it is possible to simultaneously receive and process signals with the two or more microwave frequencies used at the time. This means that the receiver branches to a certain extent have to be doubled (for co-operation between two radar units), but certain broad band units (such as antennas) can, however, be in common. The American patent U.S. Pat. No. 3,161,870 and also to a certain extent the American patent U.S. Pat. No. 5,302,955 show such systems. It can, however, be considered to be a disadvantage that each radar unit that is included in a frequency division multiplexing system has to include an extra receiver branch for each radar unit that is included in the system. From the space aspect alone a frequency division multiplexing system is therefore probably not a realistic way of increasing the performance of airborne radar systems. It can also be considered to be a disadvantage that a system with three co-operating radar units requires three receiver branches in each radar unit, which results in an extremely expensive system. It can also be considered to be a disadvantage that a frequency division multiplexing system is a hardware-dependent system which results in a very inflexible system which can possibly be accepted in a permanent ground-based system. The fact that a frequency division multiplexing system is a hardware-dependent system means that it must be determined in advance which radar units are to be included in such a system and also how many radar units are to be included in each system.